Chronic exposure to benzene results in rats in the decrease of the lymphocyte count in the peripheral blood, the decrease of the beta-glucuronidase (BG) activity both in lymphocytes and neutrophilic granulocytes as well as in the damage to lysosomal apparatus of lymphocytes expressed in diffusion of the enzyme within the cell cytoplasm. Administration of selenium (sodium selenate) in dosis of 1.0 microgram/Kg during consecutive 10 days prior the exposure to benzene resulted in prevention of benzene-induced decrease of the BG activity in granulocytes and of a damage to lymphocyte lysosomes. Application of selenium in dosis of 5.0 microgram/Kg during the same time prior the exposure to benzene prevented the benzene-induced lymphocytopenia, induced the reactive increase of the granulocyte number, and caused, moreover, the prevention of the BG activity decrease in granulocytes. Simultaneously the increase of the BG-positive lymphocyte percentage was noted which was related to the increase of cells exhibiting the cytoplasmatic and extralysosomal localization of the enzyme. The results suggest that only smaller doses of sodium selenate prevented the damage to lysosomal membrane of lymphocytes induced by toxic effect of benzene.